Prognostic Meteorological Discussion
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FXUS02 KWBC 071614
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1114 AM EST WED DEC 07 2016

VALID 12Z SAT DEC 10 2016 - 12Z WED DEC 14 2016

...PATTERN OVERVIEW AND GUIDANCE PREFERENCES...

THE WPC MANUAL PRODUCT SUITE WAS PRIMARILY DERIVED FROM A BLEND OF
THE EXPERIMENTAL 00 UTC GFS PARALLEL RUN AND 00 UTC GEFS/ECMWF
ENSEMBLE MEANS. THE PARALLEL RUN IS BEING EVALUATED FOR EMC
IMPLIMENTATION AND OFFERS A SOLUTION COMFORTABLY BETWEEN THE
OPERATIONAL 00 UTC GFS/ECMWF. THIS SOLUTION MAINTAINS GOOD WPC
CONTINUITY...TAKES INTO ACCOUNT LATEST MODEL TRENDS...AND IS WITH
CONDIERATION OF INCREASED SHORT AND MEDIUM RANGE UNCERTAINTY
ASSOCIATED WITH A PATTERN INHERENT WITH A SERIES OF EMBEDDED
SMALLER SCALE FEATURES WITHIN GENERALLY FLATTENED AND PROGRESSIVE
FLOW DEVELOPMENT OVER THE LOWER 48.

ON DAYS 3-4 AGREEMENT IS GOOD WITH AN AREA OF LOW PRESSURE JUST
OFF THE PACIFIC NORTHWEST COAST ALONGED WITH A STATIONARY FRONTAL
DRAPE EXTENDING INLAND ACROSS THE NORTHERN ROCKIES TO A FRONTAL
SYSTEM DEVELOPING ON THE IN CENTRAL ROCKIES THEN PLAINS THAT MOVES
NORTHEAST TOWARDS THE UPPER MS VALLEY AND GREAT LAKES SUN 11 DEC.
GUIDANCE DIFFERENCES GROW SUN INTO MON AS THE LOW MOVES INTO
SOUTHEAST CANADA WITH A TRAILING AND WAVY COLD FRONT MOVING ACROSS
THE NORTHEAST TO THE OH VALLEY AND APPALACHIANS. THE ECMWF SHOWS
LESS EMPHASIS WITH THIS LOW THAN RECENT OPERATIONAL GFS RUNS AND
INSTEAD DEVELOPS A MORE ORGANIZED AND PCPN FOCUSING NEW WAVE BACK
ALONG A LESS PROGRESSIVE FRONTAL PUSH OVER THE E-CENTRAL TO E/SERN
US. THE PARALLEL GFS OFFERS MORE EVEN LOW DEVELOPMENT AMID
UNCERTAIN SUPPORTING FLOW ALOFT.

FOLLOWING THESE SYSTEMS WILL BE MODEST COLD AIR INTRUSION FOLLOWED
BY A MORE AMPLE SURGE OF COLD CANADIAN/ARCTIC AIR FROM SOUTHWEST
CANADA INTO NRN WRN US/ROCKIES EARLY NEXT WEEK THAT SURGES THROUGH
THE PLAINS AND EAST-CENTRAL US INTO DAYS 6/7.

ADDITIONAL SPREAD DEVELOPS OVER THE EASTERN PACIFIC AND ADJACENT
POSITIONS OF THE PACIFIC NORTHWEST AND NORTHERN CA AS THE
ECMWF/GFS/CANADIAN GLOBAL ALL SHOW LOW PRESSURE DEVELOPING ON A
WAVY SURFACE FRONT WITH EACH MODEL INDICATING A DIFFERING CYCLONE
TRACK/SPEED/INTENSITY. THIS LEADS TO STRONG ONSHORE FLOW AND A
POTENTIAL HEAVY PRECIP EVENT OVER OR/NRN CA.

...WEATHER HIGHLIGHTS/THREATS...

OVER THE WEST THE LARGE SCALE PATTERN WILL LIKELY PROMOTE
PERSISTENT VALLEY RAIN AND INLAND/HIGHER ELEV SNOW ACROSS THE
PACIFIC NORTHWEST/NRN CA/NORTHERN GREAT BASIN/NORTHERN ROCKIES
WITH A PRONOUNCED COASTAL/TERRAIN FOCUS FOR HIGHEST AMTS. THE
POTENTIAL EXISTS FOR ONE OR MORE EPISODES OF LOCALLY HVY
PCPN...MOST LIKELY OVER NRN CALIFORNIA AND/OR WRN OREGON. ABOVE
NORMAL TEMPS PERSISTS IN THE DESERT SOUTHWEST THROUGH THE WEEKEND
AND EARLY NEXT WEEK BUT BECOME BELOW NORMAL IN THE CENTRAL TO
NORTHERN GREAT BASIN/CENTRAL TO NORTHERN ROCKIES/PACIFIC
NORTHWEST.

WITH THE FORECAST ARCTIC SURGE COMING OUT OF SOUTHWEST CANADA INTO
THE NORTHERN PLAINS...AN IMPRESSIVE AREA OF TEMPERATURES WELL
BELOW NORMAL DEVELOPS IN THE NORTHERN HIGH PLAINS AND
SPREADS/MODIFIES SOUTHWARD/EASTWARD.

THE WEEKEND SYSTEM TRAVERSING FROM THE CENTRAL PLAINS TO UPPER MS
VALLEY/UPPER LAKES HAS POTENTIAL TO PRODUCE SOME LOCALLY HEAVY
SNOW ALONG THE STORM TRACK...WITH LIGHTER AMOUNTS IN THE
DOWNSTREAM WARM ADVECTION ACROSS THE LOWER LAKES AND NORTHEAST.
WAVES ALONG THE TRAILING FRONT WOULD ALSO BE ABLE TO TAP LEADING
POOLED MOISTURE FOR SOME MODEST RAINFALL. MEANWHILE...HEAVY SNOWS
ARE ALSO EXPECTED OVER WIDESPREAD FAVORED TERRAIN OF MUCH OF THE
NWRN QUARTER OF THE US AS PACIFIC IMPULSES MOVE OVER THE REGION TO
ENHANCE LOCAL MOISTURE/LIFT.

SCHICHTEL

$$




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